1. Field of the Invention
The present invention relates to an ink-jet printing method and an ink-jet printing apparatus which can maintain a clearance between a printing surface and an ink-jet head and attitude of the ink-jet head, for printing objects of various thickness.
2. Description of the Related Art
In an ink-jet system, ink droplet is ejected from ink ejection openings formed in an ink-jet head toward a printing surface of a printing object for printing a desired information on the printing surface of the printing object. Therefore, it is important for assuring satisfactory printing quality to maintain the clearance between the ink ejection openings of the ink-jet head and the printing surface of the printing object.
Conventionally, since sheet form paper having a thickness of about 0.15 to 0.2 mm or the like is exclusively considered as the printing object, it has been sufficient to mechanically set the clearance between the ink ejection openings of the ink-jet head and the printing surface of the printing object for enabling printing on the paper of the like or typical thickness.
Printing apparatuses having mechanisms for adjusting distance between the ink-jet head and the printing object in accordance with the various kinds of the printing objects also are know. However, the adjustable range is merely set to accomodate the thickness of paper, such as a cardboard or the like, at the maximum. Namely, there has been no printing apparatus which can appropriately adjust the clearance between the ink-jet head and the printing surface of the printing object for a variety of printing objects, such as timber, resin, metal and so forth.
In the recent years, study has been made to perform printing of desired image information on a cloth or so forth, or to perform application of an etchant on a metal plate and so forth for forming a printing plate or so forth, utilizing the feature of an ink-jet system, with timber, resin or metal.
To perform ink-jet printing for such wide variety of printing objects, it is inherently required to provide a mechanism for adjusting the clearance between the ink ejection opening of the ink-jet head and the printing surface of the printing objects. In view of this, as is well known from Japanese Patent Application Laid-open No. 219520/1989, there have been proposed ink-jet printing apparatuses which incorporate mechanisms for adjusting clearances between the ink ejection openings of the ink-jet head and the printing surface of the printing objects.
However, in the case of the ink-jet printing apparatus disclosed in Japanese Patent Application Laid-open No. 219520/1989, a sensor for adjustment of the clearance is constantly held in contact with the printing surface of the printing object, which may form scratch lines or stain the printing surface in some case.
On the other hand, conventional ink-jet printing apparatuses may perform printing or printing objects having a uniform thickness. Thus, for a printing object which has a variable thickness, such as a wedge shaped printing object, printing on the printing surface has been considered impossible unless a certain jig is employed.
Furthermore, in the case of special printing objects other than paper, such as timber, metal and so forth, the operator has to position the printing object relative to a predetermined position of the ink-jet printing apparatus. However, conventional ink-jet printing apparatuses have not been designed in consideration of such special printing objects, and thus have no appropriate positioning device. Therefore, some measurement has been required.